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Soil Erosion: The Land's Carbon Conveyer Belt
Ritchie, J.C. and McCarty, G.W.  2003.  137Cesium and soil carbon in a small agricultural watershed.  Soil & Tillage Research 69: 45-51.

In the words of the authors, "recent studies indicate that soil erosion and redeposition may establish an ecosystem disequilibrium that will promote carbon sequestration within the biosphere (Stallard, 1998; Harden et al., 1999)."  In this scenario, "soil erosion on the uplands moves soil carbon to deposition sites on the landscape and promotes soil carbon replacement at the eroded sites from the production of vegetative biomass."  Often, the deposition sites are riparian systems with high net primary productivity, which also leads to increased onsite storage of carbon.  With respect to the validity of these concepts, Ritchie and McCarty note that "the capacity of riparian and flood plain systems to capture sediments has been documented (Ritchie et al., 1975; Walling et al., 1999) as well as the ability of these systems to store carbon has been documented (Lal et al., 1998)."

What was done
The authors collected -- and analyzed for carbon content -- profiles of soils from an upland area and an adjacent riparian system, into which the upland area drains, at the USDA's Beltsville Agricultural Research Center near Beltsville, MD, USA.

What was learned
The riparian system was found to act as a filter, removing eroded soil materials from the overland flow before they reached the stream that drains the area.  Hence, soil carbon was significantly greater in the riparian soils than in the upland soils.  In fact, Ritchie and McCarty determined that carbon storage in the riparian soils was 3.8 times greater than that in the upland soils in the upper 20 cm of the soil profile and 4.7 times greater in the upper 30 cm, while they report that the work of Ritchie and McCarty (2001) suggests "there may be as much as 10-15 times more carbon in the total profile (0-200 cm) of the riparian soils."

What it means
As we said with respect to the study of McCarty and Ritchie (2002) in one of our Carbon Sequestration Commentaries, "the findings of this new study are highly welcome, as they put a bright new face on what was long believed to be a phenomenon of absolutely no virtue whatsoever, i.e., soil erosion."  In addition, they "provide a wholly new reason for protecting earth's wetlands, i.e., preserving an important sink for atmospheric CO2."  Last of all, the findings of Ritchie and McCarty lay the groundwork for a system that may one day be actively promoted by the government and used by farmers to sequester carbon in an overt attempt to slow the rate of rise of the air's CO2 content that has some virtue in and of itself.

Harden, J.W., Sharpe, J.M., Parton, W.P., Ojima, D.S., Fries, T.L., Huntington, T.G. and Dabney, S.M.  1999.  Dynamic replacement and loss of soil carbon on eroding cropland.  Global Biogeochemical Cycles 14: 855-901.

Lal, R., Kimble, J.M., Follett, R.F. and Cole, C.V.  1998.  The Potential of US Cropland to Sequester Carbon and Mitigate the Greenhouse Effect. Ann Arbor Press, Chelsea, MI.

McCarty, G.W. and Ritchie, J.C.  2002.  Impact of soil movement on carbon sequestration in agricultural ecosystems.  Environmental Pollution 116: 423-430.

Ritchie, J.C. and McCarty, G.W.  2001.  Sediment deposition rates and carbon content in the soils of an agricultural riparian ecosystem.  Proceedings of the Seventh Federal Interagency Sedimentation Conference 2: IX41-IX46.

Ritchie, J.C., Hawks, P.H. and McHenry, J.R.  1975.  Deposition rates in valleys determined using fallout Cs-137.  Geological Society of America Bulletin 86: 1128-1130.

Stallard, R.F.  1998.  Terrestrial sedimentation and the carbon cycle: coupling weathering and erosion to carbon burial.  Global Biogeochemical Cycles 12: 231-257.

Walling, D.E., Owens, P.N. and Leeks, G.J.L.  1999.  Rates of contemporary overbank sedimentation and sediment storage on the floodplains of the main channel systems of the Yorkshire Ouse and River Tweed, UK.  Hydrological Processes 13: 993-1009.

Reviewed 1 October 2003